Earth's Second 'Moon' Has A Hypnotically Weird Orbit

Astronomers are increasingly learning that all of our most common models of the solar system are way, way too simple. Whether it’s dwarf planets popping up in asteroid belts with mysterious bright lights on the surface, or the relatively recent presence of a second star, everything is turning out to be a lot more complex than eight simple planets orbiting one, nice sun.

Discovered first in 1997, 3751 Cruithne is a chunk of rock about 5km across, which loops around the Earth in a ridiculously beautiful and complicated ‘horseshoe’ orbit once every 800 years. In fact its orbit is so large that it actually comes close to both Venus and Mars as well as Earth, but it does seem to be uniquely linked to our own orbital path. And it’s not alone - astronomers think there could be many more such objects that ‘belong’ to the Earth, and that studying them could be a crucial way to learn how the solar system evolved. It could also be a place to land human astronauts, given that it is actually (at various points) relatively close to us.